I was watching this video of a live chicken trapped on a moving truck and thought it was strange that it’s not possible to say anything to them even when circumstances might warrant it. All we got is honking and waving. There could be a touchscreen interface with a map of nearby vehicles. It could be voice controllable or the passenger could do it for safety.
Seconded on their usefulness on the road. Incredibly easy to just reach over, hold the PTT button and get your message across. One time purchase for something that won’t get shut down or unsupported ever.
If you try communicating with a phone, the only safe way to do it (assuming one person per vehicle) is to start a phone call before leaving, and keep it running constantly. If you have a passenger, they become your secretary. If the call drops then that’s all comms lost until both pull over and redial. Requires mobile coverage everywhere on your route which in Australia isn’t the case, even on major routes like A1 Bruce Highway.
Walkie talkies are king for travelling with mates